Interpretive Summary: Small ruminant lentiviruses include viruses that primarily infect sheep and goats (ovine lentivirus [OvLV]; also known as ovine progressive pneumonia virus/maedi-visna virus, and caprine arthritis encephalitis virus [CAEV], respectively). These viruses result in production losses and increased costs for both sheep and goat agriculture around the world. Breed differences in fraction of sheep infected and control of virus once infected with OvLV had suggested a role for genetics. Recently, a genetic marker test for sheep susceptibility to OvLV has been developed based on the TMEM154 gene. While no single version of the TMEM154 gene yet has been shown to confer complete resistance to OvLV, consistent association in thousands of sheep from multiple breeds and management conditions highlight a new strategy for intervention to limit viral spread and damage by selective breeding. This genetic marker-assisted selection (MAS) has the potential to be a useful addition to existing viral control measures. Further, the discovery of multiple additional gene regions associated with susceptibility to or control of OvLV suggests that additional genetic marker tests may be developed in the future. This review will cover both the strengths and limitations of existing data about host genetics as an intervention to control small ruminant lentiviruses, and then outline additional questions for future research in both sheep and goats.

Technical Abstract:
Small ruminant lentiviruses include members that infect sheep (ovine lentivirus [OvLV]; also known as ovine progressive pneumonia virus/maedi-visna virus) and goats (caprine arthritis encephalitis virus [CAEV]). Breed differences in seroprevalence and proviral concentration of OvLV had suggested a strong genetic component to susceptibility and control of OvLV infection in sheep. A genetic marker test for susceptibility to OvLV has been developed recently based on the TMEM154 gene with validation data in many sheep flocks. While no single genotype has been shown to have complete resistance to OvLV, consistent association in thousands of sheep from multiple breeds and management conditions highlight a new strategy for intervention by selective breeding. This genetic marker-assisted selection (MAS) has the potential to be a useful addition to existing viral control measures. Further, the discovery of multiple additional genomic regions associated with susceptibility to or control of OvLV suggests that additional genetic marker tests may be developed to extend the reach of MAS in the future. This review will cover both the strengths and limitations of existing data from host genetics as an intervention and then outline additional questions for future research in both sheep and goats.